network-problem.md

I have a service running on a LAN that are also exposed over the WAN, say Service A is reachable under example.com and it’s running on Host A in the LAN. The way this is implemented is port forwarding in the WAN gateway in the LAN:

public_ip:80 -> host_a_ip:80

Now I have a laptop that is often in the LAN, but not always. When that laptop is in the LAN, it can’t reach example.com, because the gateway port forwarding doesn’t work for internal requests (and their is no option to add/enable this). I also can’t replace the gateway router. So when that laptop wants to access example.com while in the LAN, it has to use the internal LAN ip of Host A.

Rest assured this is annoying. How can I make it, so the laptop can reach example.com regardless of whether it is in the LAN or not?

Options:

1. DNS trickery: Make example.com resolve to the local ip instead of the remote one. How do I set that up for Mac OS X? Would prefer not to have to set up my own DNS server, but would if it helped.

2. IP routing trickery on the laptop. No idea how to do this, and how to make it transparently on/off depending on the wifi.

3. While writing this, I could make another box on the LAN the gateway for everything in the LAN which in turn then only uses the WAN router. Then I’d have more control over ip forwarding shenanigans. Then I just need to figure out how to make the gateway configuration depending on whether the client is on the LAN.

But I’d still like to know if there is a simpler option.

@nelsonmenezes thanks, I’ll check that out! :)

Probably you can simply use the dns server on your router for this? Best and cleanest solution. Also most likely the one which will result in least errors.

We used dnsmasq in a similar situation.

@deveth0 — router has no dns, can’t get a new router

@djc thanks!

@janl I'd go with the dnsmasq-based solution proposed by @klaemo. Seems like you can specify DNS servers for locations in OSX; see here.

@janl the solution with dnsmasq which @klaemo described is pretty much the same that I proposed with the custom DNS setup. The MacOS supports these settings with the different "Location" under network settings. There you could define a profile with DHCP but fixed DNS Server for your LAN. Then the only thing you'd need to do is switch to that network location profile whenever you're in the LAN. The Software "Control Plane" can help automagically detecting the network location and switch to it.

Thanks all, I’ve got dnsmasq running like a charm, this is awesome :)